Earth’s energy imbalance is associated with the forcings of the climate system and how it responds, including all of the feedbacks. EEI is actually the net outcome, but climate models facilitate the understanding of the actual flows of energy through the climate system and in turn are a key step toward estimating the consequences. Hence, climate models are extensively used to encapsulate the knowledge and understanding of the climate system and how it works, and for making projections of the future. However, as noted in Chapter 1, the models are not perfect and involve approximations and assumptions. The IPCC approach has been very democratic in that all models have been treated equally even though some models have been shown to contain substantial errors. It makes sense to use only the models that perform well. Of course, all models contain errors, but some models actually violate physical principles, such as conservation of mass or energy, and these should not be used. Certainly, some models are a lot better than others.